We can quickly see that the best paid person is the doctor, who must be Al or Charlie. The chef can’t be the best paid person, as Charlie earns more, and similarly, the fireman can’t be the best paid person, as Al earns more. By similar logic, Ben must be the worst paid person.
Irrespective of the order of the chef and the fireman, the doctor must be paid 1.08x1.12 = 1.2096 times the worst paid person. The smallest whole number that gives a whole number when multiplied by 1.2096 is 625 (which is 25x25), meaning that the doctor was paid $756. So the doctor can’t be Al, who was paid less than $750.
So Charlie is the doctor and was paid $756, Al was the chef and was paid $675, and Ben was the fireman and was paid $625.